A team of physicists has conducted an experiment to study how free fall affects the wave-like properties of atoms, tackling a long-standing question in physics. The research was led by Ron Folman from Ben-Gurion University of the Negev, with collaborators from Germany, the UK, and the US, including Nobel laureate Roger Penrose. They created a new type of interferometer—a device that can split and recombine waves to observe their properties—which is capable of placing a single atom in a superposition of two paths: one where the atom is in free fall and another where it remains still. These two paths eventually meet at the same point and time, allowing researchers to measure how free fall influences the atom’s wave-like characteristics. This experiment builds on a theory developed nearly a century ago, which aimed to understand how free fall would influence a quantum wave. If the predictions of this theory are incorrect, it could suggest a conflict between quantum mechanics and Einstein’s theory of gravity. Testing this theory has been difficult in the past due to the lack of a suitable interferometer capable of handling such delicate quantum measurements. In quantum mechanics, every particle, no matter how large, is described as having wave-like properties. These properties are characterized by a phase, which indicates whether the wave is at a peak or a trough. The researchers aim to measure how free fall changes this phase, offering new insights into the relationship between gravity and quantum behavior. The results of this experiment could have significant implications for our understanding of fundamental physics. By observing how gravity affects the wave-like nature of matter at the atomic level, scientists may uncover new information about the unification of quantum mechanics and general relativity, two theories that currently describe different aspects of the universe but have yet to be fully reconciled.